The present invention relates to the construction of an inking roller or the like and to the method of making the same.
Inking rollers, a generic term for rollers adapted to spread liquid such as ink, water, or other solvents, are essential parts of the printing and graphic arts industries. For example, water form Barback rollers are used in the printing industry to spread water over a printing plate as evenly and as thinly as possible. When water and/or other liquids are distributed over a printing plate, it covers those areas of the plate with printing images to which ink is applied for printing, as well as those areas that are free or devoid of printing images and are intended to be free of print. If the water or other liquid is applied and spreads too quickly or too unevenly, printing is adversely affected and the printed image that is produced is often unacceptable.
The problem with the known rollers, for example, lies in the fact that in order to obtain the optimum print performance, the exterior surface of the roller is required to have a certain characteristic (such as hardness, resiliency, and porosity), while the overall radial body of the roller is required to have a different characteristic (particularly hardness) necessary to withstand the forces applied to it by the supporting shaft, and the increased speed relative to the outer surface.
In particular, it is important to provide a roller having an outer or contact surface enabling the uniform spread of the ink and/or other liquid against the counter rollers and print plate, while at the same time providing overall characteristics radially from center to surface to transmit a uniform mechanical pressure on the roller itself.
Various attempts were known to provide rollers having varying characteristics of hardness, resiliency, etc. built into them. In years past, rollers were covered with fabric such as moleskin to provide the desired external surface characteristics or to provide rollers having soft surfaces or by covering a rubber base element with softer rubber materials. See for example U.S. Pat. No. 1,370,709. More recently, more complex constructions were attempted. For example, U.S. Pat. No. 4,750,422, issued to Max Gysin on Jan. 14, 1988, provided a water form roller, having a plurality of helically, interwound rubber compounds of different durometers bonded to form a monolithic roller. Another attempt has been made in U.S. Pat. No. 4,065,841, by Max Gysin, issued Jan. 3, 1978, wherein a roller was manufactured completely of polyvinylchloride (PVC) resin at a preselected hardness to withstand the pressures of printing and where the surface has been mechanically abraded to provide the desired surface characteristics.
However, it has become the industry's standard to provide rollers of rubber and/or elastomeric blends of natural or synthetic rubbers and PVC. Such rollers are blended to provide uniformity in materials and characteristics throughout their depth so as to provide a nominal durometer hardness as well as other characteristics which are somewhat between those desired on the exterior and those desired in the interior. As such, these rollers are produced neither for optimum surface application of liquid nor for optimum strength, durability, or long useful life.
There exists, therefore, the need for a water form roller which does not exhibit the foregoing disadvantages. The present invention fulfills such a need.
It is another object of the present invention to provide a roller having overall nominal characteristics such as hardness and/or resiliency in which the exterior surface of the roller is formed having specifically different characteristics from that of the concentric interior of the roller.
It is a further object to provide a roller having optimum characteristics for liquid application on its exterior surface as well as optimum characteristics in the interior to absorb the shock and strain created by its mounting or its use.
A more specific object of the present invention is to provide a roller formed of a harder, more dense composition of predetermined characteristic on the exterior and a second material of a softer more resilient different set of characteristics in the interior.
These objects, as well as other objects and advantages will be apparent from the following disclosure.